This invention relates to variable capacity vane compressors which are adapted for use as refrigerant compressors of air conditioners for automotive vehicles, and more particularly to variable capacity vane compressors of this kind in which the timing of commencement of compression is varied to thereby control the capacity of the compressor.
Such a variable capacity vane compressor is known e.g. by Japanese Provisional Patent Publication (Kokai) No. 62-20688 assigned to the same assignee of the present application. The above conventional vane compressor basically comprises a cylinder formed of a cam ring and a pair of side blocks closing opposite ends of the cam ring, one of the front and rear side blocks having at least one first inlet port formed therein; a rotor rotatably received within the cylinder; a plurality of vanes radially slidably fitted in respective slits formed in the rotor; wherein compression chambers are defined between the cylinder, the rotor and adjacent ones of the vanes and vary in volume with rotation of the rotor for effecting suction of a compression medium from the suction chamber into the compression chambers through the at least one first inlet port, and compression and discharge of the compression medium; at least one second inlet port formed in the on of the front and rear side blocks which has the at least one first inlet port formed therein; a pressure chamber formed in the one of the front and rear side blocks and communicating with a zone under lower pressure and a zone under higher pressure; a control element angularly displaceably fitted within an annular recess formed in the one of the front and rear side blocks, for controlling the opening angle of the at least one second inlet port, the control element having a pressure receiving portion slidably fitted in the pressure chamber and dividing the pressure chamber into a first pressure chamber communicating with the zone under lower pressure and a second pressure chamber communicating with both the zone under lower pressure and the zone under higher pressure chamber; the control element being angularly displaceable in response to a difference in pressure between the first and second chambers for causing the control element to vary the opening angle of the second inlet port, to thereby cause a change in the timing of commencement of the compression of compression medium and hence vary the capacity of the compressor; and a biasing member loosely fitted around a hub projecting integrally from the one of the side blocks at one end face remote from the rotor, for biasing the control element in a direction of increasing the opening angle of the at least one second inlet port.
However, according to this conventional vane compressor, the biasing member is formed by a torsion coiled spring, for example, which has a coiled body thereof fitted around the hub projecting integrally from the one of the side blocks at one end face remote from the rotor, with one end thereof engaged with the control element and the other end engaged thereof with the hub, respectively. With such arrangement, the coiled body of the torsion coiled spring can have loops thereof brought into contact with each other, or can be brought into contact with the outer peripheral surface of the hub since the ends of the torsion coiled spring are loosely supported by the control element and the hub of the one side block, thus undesirably causing a frictional force. This frictional force possibly results in a hysteresis between deformation of the torsion coiled spring toward its tensioned position and resumption of same back to its relaxed position, thereby making it difficult to accurately control the control element and hence the capacity of the compressor.